The present invention relates to an effective technology for applying to a high frequency power amplifier circuit and an electronic component for a high frequency power amplifier that incorporates this high frequency power amplifier circuit, and, in particular, relates to a technology that realizes a stable amplifying characteristic in the high frequency power amplifier circuit for supplying an amplifying transistor with a bias by a current mirror method.
A high frequency power amplifier circuit (having multi-stage composition usually) that uses a semiconductor amplifying device, such as a MOSFET (insulated gate field-effect transistor) or a GaAs-MESFET is incorporated in the transmitting-side output unit of a radio communication system (mobile communication system), such as a cellular phone.
This high frequency power amplifier circuit is, usually, constructed in most cases as a single electronic component. In the electronic component, a semiconductor chip including an amplifying transistor and its bias circuit is mounted on an insulating substrate, such as a ceramic substrate in which printed wiring applies on the surface or in the inside, together with a discrete component such as another semiconductor chip or a capacitor, and each component is coupled by the printed wiring or a bonding wire. This electronic component is called an RF power module.
Incidentally, in the case of a semiconductor chip used in an RF power module for a cellular phone, high integration is advancing to enable the high performance and miniaturization of the module. Moreover, in recent years, from the standpoint of the stabilization of a high frequency amplifying characteristic, an invention concerning the RF power module is proposed (for example, refer to Patent Document 1). According to this invention, as shown in FIG. 12, an amplifying FET Q0 and a biasing Q1 to which a gate is connected in common are provided. A bias current Iin is generated through a current mirror circuit consisting of FETs Q3 and Q4 to which a current from a constant current source C1 is transferred. This bias current Iin applies to the biasing FET Q1 and a bias is supplied to the amplifying FET Q0 by a current mirror method, then a current Iout applies in accordance with a ratio of the widths of the Q1 and Q0.
In an RF power module that provides the amplifying FET Q0 with a bias by such a current mirror method, even if an FET threshold voltage (Vth) scatters, an idle current applied to the amplifying FET Q0 does not vary. Accordingly, as an advantage, element scattering need not be corrected, and even a yield improves. Further, when a bias is supplied to amplifying transistor by the current mirror method in a state in which a high frequency signal is not input, that is, there is no signal, a drain current applied to the amplifying transistor is referred to as the idle current in this specification.
Furthermore, an invention regarding a high frequency power amplifier circuit (refer to FIG. 13) that improves a high frequency amplifying characteristic is proposed (for example, refer to Patent Document 2). According to this invention, an FET having dual gate structure or two FETs of a series form are used as an first-stage power amplifying element of an RF power module to adjust a saturation point (the maximum current) of mutual conductance (gm) with a one-side gate voltage and to operate the RF power module in the vicinity of the saturation point.
[Patent Document 1] Japanese Unexamined Patent Publication No. 2003-017954
[Patent Document 2] Japanese Unexamined Patent Publication No.2004-193846